The present invention relates to a method of making a gas-tight connection or joint between a helically corrugated tube and a sleeve, wherein both parts are made of a high quality steel.
High quality steel pipes or tubes are used for the transport of cold or even very cold fluids. Such tubes are, for example, used in cryogenic cables. Generally speaking, tubes are made, for example, in a continuous manufacturing process in that a flexible strip or skelp is formed into a cylindrical configuration by bending it longitudinally into a split tube. The longitudinal joint along the strip edges is welded and the resulting tube is subsequently corrugated. This tube making technique is well known and has been practiced under utilization of a variety of materials including also high quality steel. The strip used for that purpose may well be of the thin gage variety having a thickness of less than a millimeter such as 0.3 to 0.8 mm.
Tubing of the type referred to above can be made in that manner basically in any length, depending only on the length of the strip or skelp being processed. On the other hand, tubing thus produced is, of course, used in finite, well defined lengths. Moreover, transporting the tubing to the installation site is possible only up to certain lengths depending on the transport facilities and other factors. Consequently, the need arises to provide for connection between ends of such tube lengths or between the end of a tube and other equipment. Generally speaking, one usually requires that a sleeve be connected to such an end to be connected further as required.
Attempts have been made to weld one front end of such a sleeve to the front end of a corrugated tube under utilization of a welding wire or filler rod. The welding area included a crest as well as a valley of the corrugation. However, it was found that in the case of high quality steel a flawless welding joint could not always be produced. The quality of welding was generally rather difficult to control. Moreover, it was frequently observed that the welding torch burnt a hole into the rather thin tube, and the welding joint became quite useless.